Method for producing water-soluble polymers, comprising oligoalkylene-imine side chains

ABSTRACT

The invention relates to a method for producing water-soluble homopolymers and copolymers, comprising oligoalkylene-imine side chains of the general formula (I), wherein [AI] m , m, Y and x have the definitions given in claim  1 , by radical homopolymerisation or copolymerisation of monomers A of the general formula (II), wherein [AI] m , m, n, Y and R have the definitions given in claim  1 , in an aqueous reaction medium. The invention also relates to the homopolymers and copolymers obtained by this method and to their use as auxiliary agents in paper production.

The present invention relates to a process for preparing water-solublehomopolymers and copolymers having oligoalkyleneimine side chains of thegeneral formula I,

where

is a linear or branched oligoalkyleneimine chain comprising malkyleneimine units, where

m is an integer from 1 to 20, and the number average of m in theoligoalkyleneimine side chains is at least 1.5,

Y is the anion equivalent of a mineral acid, and

x is 0≦x≦m,

and to the copolymers obtained by this process and their use asauxiliaries in papermaking.

In papermaking, in particular in papermaking under neutral conditions,polymers having basic amino groups, the acid addition salts thereof oramino-containing, amphoteric polymers are often employed. They are oftenused as fixing agents and as drainage aids, flocculents and retentionaids.

U.S. Pat. No. 3,280,218 describes graft polymers havingpolyalkyleneimine side chains. These polymers are prepared by reactingpolyacrylic acid as grafting base with a large excess of ethyleneimine.A disadvantage of this process is the high ethyleneimine requirement.Polymers free from acid groups cannot be prepared by this route, sincesome of the carboxylate groups do not react owing to steric effects.Furthermore, other functional groups cannot be introduced into thepolymer in this manner.

EP-A 387 567 describes polymers which are obtainable by reacting acarboxyl-containing, water-soluble polymer with ethyleneimine. Thisprocess provides polymers having oligomeric alkyleneimine side chainsand molecular weights of up to 1,000,000. As a consequence of theirmethod of preparation, such polymers likewise necessarily containcarboxylic acid groups. The amphoteric polymers described in thisreference are used as flocculents and drainage aids in papermaking.

Likewise, EP-A 411 654 describes amphoteric polymers havingaminoalkylene side groups. Similar to EP-A 387 567, they are preferablyprepared by reacting a carboxyl-containing, water-soluble polymer withethyleneimine. The polymer likewise necessarily contains acid groups.

One disadvantage of the preparation methods described in the prior artis that acid-free polymers having oligoalkyleneimine side chains cannotbe prepared in this manner. Furthermore, the molecular weight of thepolymers obtainable in this manner depends on the molecular weight ofthe grafting base used. There is an upper limit for the latter molecularweight, since otherwise this causes viscosity problems that inhibit oreven prevent the reaction with the ethyleneimine. Furthermore, it hasbeen observed that relatively high molecular weights of the graftingbase lead to gel formation, even at low ethyleneimine conversions, thusalso limiting the maximum achievable molecular weight. This method doesnot permit controlled adjustment of chain lengths with the oligomericalkyleneimine side chains either.

We have found, surprisingly, that water-soluble polymers havingoligoalkyleneimine side chains of the general formula I defined at thebeginning can be prepared by polymerizing at least one ester of theformula II which can also be used in the form of an oligomer mixture,

 and where

m and Y are as defined above, the number average of m in the oligomermixtures of II being at least 1.5,

R is hydrogen or C₁-C₄-alkyl, and

n is 1≦n≦m,

 alone or together with other monomers in water using free-radicalpolymerization initiators, and that this process yields polymers whichmeet the requirements made on paper auxiliaries to a particular extent.If polymerized on its own, monomers A yield homopolymers which haveoligoalkyleneimine side chains of the formula I, are acid-free and havea particularly high cationic charge density.

The present invention therefore provides a process for preparingwater-soluble homopolymers or copolymers having oligoalkyleneimine sidechains of the general formula I defined at the beginning, whichcomprises polymerizing ethylenically unsaturated monomers M, comprising:

at least one monomer A of the above-defined general formula II or anoligomer mixture of monomers of this type and

optionally one or more water-soluble monomers B which are different fromsaid monomers A and/or monomers C which are different from said monomersA and B,

in an aqueous polymerization medium in the presence of an initiatorwhich triggers the free-radical polymerization of the monomers M.

Linear oligoalkyleneimine structural units

are best described by the following structural formula Ia

where m is as defined above and R′ and R″ are monovalent organicradicals, such as C₁-C₄-alkyl or phenyl, or hydrogen. R′ and R″ arepreferably hydrogen.

Branched oligoalkyleneimine structural units

can be described, for example, by the following structural formula Ib

where p is 0 or an integer 1, 2, 3 . . . which is different from 0, qand r are each, independently of one another, integers which aredifferent from 0, and the sum p+q+r+1=m. Ib represents a singly branchedoligoalkyleneimine unit

It will be appreciated that the present invention also covers thepreparation of polymers in which the oligoalkyleneimine unit

is branched more than once.

The monomers A of the general formula II are usually oligomer mixturesof such compounds. In this case, m represents the number ofethyleneimine repeating units in the respective molecules of the generalformula II; according to the invention, m in these molecules is from 1to 20 and preferably from 1 to 10. According to the invention, thecomposition of the oligomer mixtures of compounds of the general formulaII is selected such that the number average of m in these mixtures is atleast 1.5, preferably at least 2.1, and is, for example, in the rangefrom 1.5 to 15, preferably in the range from 2.1 to 8 and in particularin the range from 2.5 to 4.5. According to the invention, preference isgiven to those oligomer mixtures which comprise less than 25% by weightof compounds of the general formula II where m=1. If monomers A in theform of chemically uniform compounds of the general formula II are used,m is naturally at least 2, so as to ensure a number average of m in therange of at least 1.5.

In the monomers of the general formula II, at least one of the nitrogenatoms contained therein, preferably more than one or all of the nitrogenatoms contained therein, are present in protonated form. The monomers Aare thus formally acid addition compounds. The anion equivalentsrequired for charge neutrality are usually derived from low molecularweight acids, in particular from mineral acids such as hydrochloricacid, sulfuric acid or nitric acid. This means that Y— is preferablyCl—, HSO₄—, ½ SO₄ ²—, NO₃—, H₂PO₄—, ½ HPO₄ ²— or ⅓ PO₄ ³—. Particularlypreferably, Y— is Cl—, ½ SO₄ ²— and NO₃— and in particular Cl—.

Provided that the number average of m≧2.1, the number average of n ispreferably at least 2.

In the formula II, R is preferably hydrogen or in particular methyl. Rand R′ in the formulae Ia and Ib are preferably hydrogen.

Preference is given to using the monomers A in the form of oligomermixtures of the formula II. In this case, preference is given to thoseoligomer mixtures which comprise less than 25% by weight of compounds ofthe formula II where m=1. This is usually the case when the averagevalue of {overscore (m)}≧2.1.

According to the invention, at least one further water-soluble monomerB, which is different from the monomers A, can be copolymerized togetherwith the monomer A. The solubility of the monomer B in water istypically at least 50 g/l at 25° C. and in particular at least 100 g/lat 25° C. and 1 bar. The monomers B comprise neutral monomers (monomersB1), acidic monomers (monomers B2) and/or cationic monomers (monomersB3).

Examples of neutral monomers B1 are amides of monoethylenicallyunsaturated carboxylic acids, e.g. acrylamide and methacrylamide,hydroxyalkyl esters of ethylenically unsaturated carboxylic acids, e.g.hydroxyethyl acrylate, hydroxyethyl methacrylate, 2- or 3-hydroxypropylacrylate, 2- or 3-hydroxypropyl methacrylate, 4-hydroxybutyl acrylateand 4-hydroxybutyl methacrylate, esters of monoethylenically unsaturatedcarboxylic acids with polyalkylene glycols or monoalkyl ethers ofpolyethylene glycols, e.g. esters of acrylic acid or methacrylic acidwith polyethylene glycol, polypropylene glycol, polyethyleneglycol/polypropylene glycol block copolymers, and acrylonitrile ormethacrylonitrile.

Further monomers B1 are N-vinyllactams such as N-vinylpyrrolidone andN-vinylcaprolactam, open-chain N-vinylamides such as N-vinylformamide,and vinylimidazole and 2-methyl-1-vinylimidazole.

Examples of B2 are monoethylenically unsaturated monocarboxylic acidsand monoethylenically unsaturated dicarboxylic acids such as acrylicacid, methacrylic acid, crotonic acid, isocrotonic acid,acrylamidoglycolic acid, maleic acid, itaconic acid, citraconic acid;and monoethylenically unsaturated sulfonic acids such as vinylsulfonicacid, allylsulfonic acid, methallylsulfonic acid, styrenesulfonic acidor acrylamidomethylpropanesulfonic acid or salts thereof, in particularsodium salts thereof, monoethylenically unsaturated phosphonic acids orphosphoric acids such as vinylphosphonic acid, allylphosphonic acid,methallylphosphonic acid, acryloxyethylphosphonic acid,acryloxyethylphosphoric esters, methacryloxyethylphosphonic acid ormethacryloxyethylphosphoric esters or salts thereof, in particularsodium salts or ammonium salts thereof.

Examples of cationic monomers B3 are quaternization products ofN-vinylimidazole, of aminoalkylamides and aminoalkyl esters ofmonoethylenically unsaturated carboxylic acids, e.g.dimethylaminoethylacrylate quarternized with dimethyl sulfate or methylchloride, quaternized dimethylaminoethylmethacrylate,dimethylaminopropylacrylamide and dimethylaminopropylmethacrylamide.

In a particular embodiment of the present invention, from 5 to 50% byweight, in particular from 10 to 40% by weight, of monomers A and from50 to 95% by weight, in particular from 60 to 90% by weight, of monomersB are used in the preparation of the polymers of the invention.

Preferred monomers B are neutral, water-soluble monomers B1, inparticular amides of monoethylenically unsaturated monocarboxylic acids,open-chain vinylamides such as N-vinylformamide and N-vinyllactams, inparticular acrylamide and methacrylamide and most preferably acrylamideas sole monomer B.

It is thus preferred for the monomers B to be polymerized to compriseless than 20% by weight and in particular less than 10% by weight, basedon the total weight of the monomers M to be polymerized, of monomers B2or monomers B3.

In the process of the invention, it is of course also possible tocopolymerize, in addition to the monomers A and the monomers B, othermonomers C which are different from the monomers A and monomers B. Ifdesired, monomers C are typically used in the process of the inventionin an amount of up to 40% by weight, e.g. in an amount of from 0.01 to40% by weight. However, in preferred embodiments of the process of theinvention, monomers C will be used in an amount of not more than 30% byweight, in particular of not more than 20% by weight, and particularlypreferably of not more than 10% by weight. In a particularly preferredembodiment of the process of the invention, no monomers C are used.

Monomers C include diethylenically or polyethylenically unsaturatedmonomers C1. These monomers cause crosslinking of the growing polymerchange during the polymerization and thus an increase in the molecularweight of the water-soluble polymers of the invention. Crosslinkingmonomers are typically used in an amount of from 1 to 10,000 ppm, inparticular in an amount of from 1 to 1000 ppm, in each case based on thetotal monomer amount. Examples of crosslinking monomers C1 are esters ofacrylic acid or methacrylic acid with polyols such as butanedioldiacrylate, trimethylolpropane triacrylate, tri- and tetraethyleneglycol diacrylate, and the corresponding methacrylates and thecorresponding vinyl ethers and allyl ethers of the abovementioned diolsor polyols. Further examples of monomers C1 are N,N′-divinylurea,N,N′-divinylimidazolidone, methylenebisacrylamide and allylmethacrylate, diallyl phthalate and divinylbenzene. Preference is givento those monomers C1 which have a solubility in water of >50 g/l at 25°C.

The abovementioned monomers C1 are usually used together with chaintransfer agents (regulators). The amount of chain transfer agent usednaturally depends on the efficiency of the chain transfer agent andusually is in the range from 0.0001 to 5% by weight, based on the totalmonomer amount. Examples of chain transfer agents are: aliphaticmercaptans such as C₆-C₁₂-alkylmercaptans, such as n-hexylmercaptan,n-octylmercaptan, tert-octylmercaptan, 2-ethylhexylmercaptan,n-decylmercaptan, 2-propylheptylmercaptan, n-dodecylmercaptan andtert-dodecylmercaptan; water-soluble mercaptans such as2-mercaptoethanol, mercaptopropanol, mercaptobutanol, mercaptopropionicacid and mercaptoacetic acid, and formic acid, isopropanol, allylalcohols, aldehydes such as butyraldehyde, halogenated hydrocarbons suchas chloroform, bromoform, carbon tetrachloride and the like.

In the process of the invention, it is of course also possible tocopolymerize other monomers C which are different from theabovementioned monomers (monomers C2). The monomers C2 are monomerswhich can be copolymerized with the abovementioned monomers in anaqueous reaction medium, for example vinyl esters of aliphaticC₁-C₄-monocarboxylic acids such as vinyl formate, vinyl acetate, vinylpropionate and vinyl butyrate, esters of acrylic acid or methacrylicacid with C₁-C₄-alkanols such as methyl acrylate, methyl methacrylate,ethyl acrylate and propyl acrylate, vinylaromatic monomers such asstyrene and α-methylstyrene; and esters of acrylic acid and methacrylicacid with long-chain alkanols such as lauryl (meth)acrylate and stearyl(meth)acrylate. The monomers C2 are usually used in an amount of up to20% by weight, e.g. from 0.1 to 20% by weight. In a preferred embodimentof the process of the invention, no monomers C2 are used in thepreparation of the copolymers of the invention.

According to the invention, the monomers A, B and optionally C arepolymerized in an aqueous polymerization medium. An aqueouspolymerization medium is to be understood as water and mixtures of waterand a water-miscible solvent, the amount of solvent being less than 20%by weight, based on the total amount of solvent and water. Examples ofwater-miscible solvents are C₁-C₄-alkanols such as methanol, ethanol,n-propanol, isopropanol, n-butanol or tert-butanol, and open-chain orcyclic amides such as acetamide, N,N-dimethylacetamide,N,N-dimethylformamide, N-methylpyrrolidone, and acetone andtetrahydrofuran. The aqueous reaction medium preferably contains lessthan 10% by weight, in particular less than 5% by weight, mostpreferably less than 2% by weight of water-miscible, organic solvent,and in particular none at all.

In a most preferred embodiment of the present invention, thepolymerization is carried out in water.

The process of the invention can also be carried out in an aqueouspolymerization medium which is present in emulsified form as awater-in-oil emulsion in a liquid organic medium which in turn is inertunder the polymerization conditions. The actual polymerization takesplace in the water droplets, so that polymerization conditions applywhich are essentially similar to conventional polymerization in aqueouspolymerization media.

Examples of organic liquids, which are not miscible with water and areinert under polymerization conditions, are aliphatic hydrocarbons, e.g.C₅-C₁₂-alkanes such as pentane, hexane, octane, isooctane, decane,dodecane, paraffins and isoparaffins, cycloalkanes such as cyclohexane,cyclohexanes substituted with C₁-C₄-alkyl, cycloheptane, cyclooctane,perchlorinated hydrocarbons such as perchloroethylene,1,1,1-trichloromethane and aromatic hydrocarbons such as benzene,toluene, ethylbenzene, xylenes, cumenes etc. Preferred organic liquidsare mixtures of saturated hydrocarbons, essentially consisting ofn-paraffins and isoparaffins and containing up to 20% by weight ofnaphthenes. The proportion of the water-immiscible organic liquid in thewater-in-oil emulsion is usually in the range from 30 to 90% by weight.

The water droplets in the inert organic liquid are usually stabilized byusing surfactants which are suitable for water-in-oil emulsions, forexample esters of glycerin or sorbitan with fatty acids such as sorbitanmonooleate, sorbitan monostearate, sorbitan monopalmitate, sorbitanmonolaurate, glycerol sorbitan fatty esters, ethoxylation products ofglycerol sorbitan fatty esters, and mannitol fatty esters such asmannitol monooleate, salts of monoesters of phthalic acid with fattyalcohols such as sodium hexadecyl phthalate, sodium cetyl phthalate,sodium stearyl phthalate, metal soaps such as magnesium, calcium,lithium, zinc or aluminum lanolate, stearate, laurate; polyethyleneoxides, polypropylene oxides and ethylene oxide/propylene oxide blockcopolymers, ethoxylated fatty alcohols and ethoxylated ethers ofglycerol with 1 or 2 mol of fatty alcohol (cf. EP-A 374 646). Furthersurfactants suitable for stabilizing water-in-oil emulsions are knownfrom the literature and can be taken from “Das Atlas HLB-System”Atlas-Chemie 1968, or determined by means of the criteria cited therein.The surfactants are usually used in an amount of from 0.1 to 10% byweight, based on the amount of organic liquid.

Processes for polymerizing water-soluble, ethylenically unsaturatedmonomers in an aqueous polymerization medium, which is present in theform of a water-in-oil emulsion in an organic liquid, have beendescribed in various instances in the prior art, for example inHouben-Weyl, Methoden der Organischen Chemie, 4th edition, Vol. E20, p.1182-1184, DE-AS 1081228, DE-AS 1081173, K. E. J. Barret et al.,Dispersion Polymerization in Organic Media, London 1975, p. 115, EP-A231 901, EP-A 262 577, EP-A 264 649, EP-A 374 646 and in U.S. Pat. No.3,284,393. The teachings given therein can be applied to thepolymerization of the monomers A and B, so that the contents of thesereferences are incorporated herein by reference.

The initiators are in principle any compounds which can trigger afree-radical polymerization of ethylenically unsaturated monomers.Examples of initiators are azo compounds, organic or inorganicperoxides, peroxodisulfuric acid salts and redox initiator systems. Inthe process of the invention, the initiator is usually employed in anamount of from 0.01 to 5% by weight, preferably in an amount of from0.05 to 2% by weight, and in particular in an amount of from 0.1 to 1%by weight, based on the amount of monomers to be polymerized. The amountof initiator used depends, as is known, on the efficiency with which theinitiator triggers the free-radical polymerization of the monomers. Whenthe polymerization is carried out in a water-in-oil emulsion, theinitiator amounts will often be lower, in particular when usinghydrophobic initiators. In this case, the amounts of initiator used are,for example, from 0.01 to 1% by weight and in particular from 0.01 to0.2% by weight, based on the monomers A, B and C used. It is of coursealso possible to trigger the polymerization by actinic radiation.

Examples of azo initiators are 2,2′-azobisisobutyronitrile,2,2′-azobis(2,4-dimethylvaleronitrile), 2,2′-azobis(2-amidinopropane)dihydrochloride and 2,2′-azobis(2-(2-imidazolin-2-yl)propane)dihydrochloride. Examples of inorganic peroxides are hydrogen peroxideand percarbonate, examples of organic peroxides are alkyl hydroperoxidessuch as tert-butyl hydroperoxide, cumene hydroperoxide, andperoxycarboxylic acid esters such as tert-butyl peroctoate and diacylperoxides such as dibenzoyl peroxide. Suitable peroxodisulfuric acidsalts are in particular sodium, potassium and ammonium salts. Examplesof redox initiator systems are systems comprising one of theabovementioned organic or inorganic peroxides, in particular hydrogenperoxide, as oxidation component, and at least one further reductioncomponent such as ascorbic acid, hydroxylamine or adducts of sulfurousacid and aldehydes, e.g. the bisulfite adduct of acetone or the sodiumsalt of hydroxymethanesulfinic acid, as reducing agent. Both theabovementioned peroxides and the redox initiator systems can be used inthe presence of redox-active transition metals such as iron, vanadium orcopper, preferably in the form of water-soluble salts.

If the polymerization is carried out in water, preference is given toemploying water-soluble initiator systems such as hydrogen peroxide,tert-butyl peroxide or salt-like azo compounds, e.g. the abovementionedhydrochlorides. If the polymerization is carried out in the water-in-oilemulsion described above, the hydrophobic initiators are at least asgood as the water-soluble initiators, or even better. Examples ofhydrophobic initiators are bisazo(alkylnitriles) such as2,2′-azobis(valeronitrile), 2,2′-azobis(2,4-dimethylvaleronitrile),2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile),2,2′-azobis(isobutyronitrile); alkyl and cycloalkyl percarbonates suchas dicyclohexyl peroxodicarbonate, di-2-ethylhexyl peroxodicarbonate,tert-butyl peroxoisopropylcarbonate; diacylperoxides such as acetylperoxide, dioctanoyl peroxide, dilauroyl peroxide, dibenzoyl peroxide;peroxy esters, in particular tert-butyl peroxycarboxylic esters such astert-butyl perpivalate, per-2-ethylhexanoate, perneodecanoate;hydroperoxides such as cumene hydroperoxide, p-menthane hydroperoxide,pinane hydroperoxide and tert-butyl hydroperoxide and peroxides such asdicumene peroxide, di-tert-butyl peroxide and di-tert-amyl peroxide.

The polymerization temperature usually depends on the initiator systemused and is often in the range from 20 to 110° C. and in particular inthe range from 25 to 80° C.

The polymerization time is usually in the range from 1 to 10 h.

The pH of the aqueous reaction medium is preferably in the range from pH0 to pH 6, in particular in the range from pH 1 to pH 4.

The reaction can be carried out in the form of a batch process, wherethe monomers to be polymerized are initially charged in the aqueousreaction medium and the polymerization initiator is added underpolymerization conditions, preferably at the rate at which it isconsumed, or initially charged in the polymerization vessel togetherwith the monomers and subsequently heated to the polymerizationtemperature.

It is of course also possible to conduct the polymerization as a feedprocess. In the feed process, at least part of the monomers to bepolymerized, preferably at least 80% and in particular virtually thetotal amount of the monomers to be polymerized, is introduced into thepolymerization reactor under polymerization conditions. In this process,the polymerization initiator is preferably introduced into thepolymerization reaction in parallel with the addition of the monomers.Preference is given to introducing the monomers into the polymerizationreaction, depending on the type of polymerization method desired, in theform of an aqueous solution or in the form of a water-in-oil emulsion.

The process of the invention yields homopolymers and copolymers havingoligoalkyleneimine side chains of the general formula I whose molecularcomposition is essentially the same as the composition of the monomersused.

The present invention provides on the one hand homopolymers of monomersA. They usually have a weight average molecular weight Mw in the rangefrom 100,000 to 3,000,000. The K value of a 0.1% strength by weightsolution (measured in 5% strength NaCl solution at 25° C.) is usually atleast 60, preferably at least 90. Homopolymers of this type have no acidgroups and therefore usually a higher cationic charge density than theprior art polymers which are obtainable by polymer-analogous reaction ofpolyacrylic acids with alkyleneimines. The cationic charge density ofthe novel homopolymers of the monomers A is at least 4 meq/g even at pH7, preference being given to homopolymers having a cationic chargedensity >4 meq/g, preferably >5 meq/g, at pH 7. The stated cationiccharge density is the number of protonated nitrogen atoms per gram ofpolymer, as can be determined by titration with potassiumpolyvinylsulfate according to the method described by D. Horn, Progr.Colloid u. Polymer Sci. 65 (1978) 251.

On the other hand the invention provides copolymers of the monomers Awith the monomers B and/or C. A distinction is made here between thosecopolymers which comprise the monomers A as main component and thosecopolymers which comprise the monomers B as main component.

In the latter copolymers, the polymerized monomers M comprise:

from 5 to 50% by weight, in particular from 10 to 40% by weight, ofmonomers A,

from 50 to 95% by weight, in particular from 10 to 60% by weight, of atleast one monomer B, preferably at least one or more of the monomers Bindicated as preferred and in particular of acrylamide as monomer B, and

from 0 to 40% by weight of monomers C which are different from saidmonomers A and B.

In the former copolymers, the polymerized monomers M comprise:

from 50 to 100% by weight of monomers A, and at least one furthermonomer selected from

from 0 to 50% by weight of one or more monomers B, and

from 0 to 40% by weight of monomers C which are different from saidmonomers A and B.

The copolymers of the monomers A, B and/or C, in particular thecopolymers of the monomers A and B, usually have a weight averagemolecular weight M_(w) of at least 2,000,000 (determined by lightscattering of a solution of 0.1 g of the polymer in 0.1 n NaClsolution). The present invention also provides copolymers of this type.

The weight average molecular weight M_(w) of the copolymers is often atleast 3,000,000. It can likewise be 5,000,000 or more, e.g. 15,000,000or up to 25,000,000.

The preferred weight average molecular weights M_(w) of the copolymerscorrespond to a Fickentscherr K value (measured as 0.1% strength byweight solution of the polymer in 5% strength by weight NaCl solution at25° C.) of at least 140, preferably at least 150, and in particular atleast 160.

The Brookfield viscosity of 1% strength by weight solutions of thecopolymers at 25° C. is usually more than 100, preferably more than 200,in particular more than 500, mPas. With regard to their use asauxiliaries in papermaking, high molecular weight products arepreferred.

The molecular composition of the copolymers of the invention naturallycorresponds to the type and composition of the respective mixture ofmonomers A and B and/or C. The process of the invention usually yieldsrandom copolymers, i.e. the structural units derived from the monomersA, B and/or C are randomly distributed over the carbon chain of thepolymeric backbone.

With regard to their use as retention aids, those polymers are preferredwhich contain polymerized monomers A, B and C in the weight percentagesindicated above as preferred. Thus, those copolymers are particularlypreferred which have from 5 to 50% by weight, in particular from 10 to40% by weight, and particularly preferably from 10 to 35% by weight, ofstructural units derived from monomers A. The proportion of structuralunits derived from monomers B is preferably from 50 to 95% by weight, inparticular from 60 to 90% by weight and particularly preferably from 65to 90% by weight, based on the total weight of the copolymer. Inpreferred copolymers, the proportion of structural elements having acidgroups derived from monomers B2 is preferably less than 20% by weightand in particular less than 10% by weight. Of these, particularpreference is given to those copolymers which comprise, in addition tomonomers A and optionally C, exclusively structural elements B derivedfrom neutral monomers B, in particular from open-chain N-vinylamides,N-vinyllactams and amides of ethylenically unsaturated carboxylic acidsand particularly preferably of acrylamide or methacrylamide.

The proportion of structural elements derived from monomers C preferablycorresponds to the proportions of monomers C indicated above aspreferred, based on the monomers M to be polymerized. In preferredembodiments, the copolymers of the invention contain no structuralelements derived from monomers C or only small amounts of structuralelements derived from monomers C1.

Furthermore, those homopolymers and copolymers are preferred which haveoligomeric alkyleneimine side chains of the general formula I and havean average degree of oligomerization of >2 which in particular does notexceed 8. The number average of m, based on all oligoalkyleneimine sidechains of the formula I present in the polymer, is thus preferably inthe range from 2.1 to 8. Particular preference is given to thosepolymers in which the number average m is in the range from 2.5 to 4.5.

Furthermore, it is preferred according to the invention if theproportion of structural units having an alkyleneimine side chain (sidechain of formula I where m=1) comprises less than 25% by weight, basedon the total amount of structural units having oligoalkyleneimine sidechains in the homopolymers and copolymers.

The homopolymers and copolymers of the invention are obtained in theform of aqueous solutions or a water-in-oil emulsion, from which theaqueous polymer solution can be separated in accordance with knownprocedures. The polymers of the invention are present in thesesolutions, depending on the pH of the aqueous solution, in unprotonatedform (i.e. x=0), in partially protonated form or in completelyprotonated form. For reasons of stability, the pH is often selected suchthat the nitrogen atoms in the oligoalkyleneimine side chains of thepolymers of the invention are present in at least partially protonatedform, preferably in a proportion of at least 25% by weight and inparticular of at least 50% by weight (i.e. x≧0.25 {overscore (m)} and inparticular x≧0.5 {overscore (m)}, where {overscore (m)} is the numberaverage of m).

The polymer content in the aqueous solutions (calculated as unprotonatedpolymer) depends on the type of preparation and is usually in the rangefrom 1 to 50% by weight, preferably in the range from 2 to 40% byweight. The preparation of the polymers by polymerization in awater-in-oil emulsion as reaction medium often yields solutions havingsolid contents ≧20% by weight, in particular ≧30% by weight, as thepolymerization in a homogeneous aqueous polymerization medium usuallyyields polymer solutions having polymer contents of <20% by weight, e.g.from 2 to 15% by weight.

A further aspect of the present invention relates to the above-definedethylenically unsaturated monomers A of the general formula II, inparticular in the form of oligomer mixtures, in which the average{overscore (m)} is at least 2.1 and in particular in the range from 2.1to 8. Monomers of this type are of particular interest as commercialforms. Of the oligomer mixtures of compounds of the formula II, thoseoligomer mixtures are preferred in which the proportion of compounds ofthe general formula II where m=1 is less than 25% by weight, based onthe total amount of compounds of the general formula II. Particularpreference is given to those monomers of the general formula II, inwhich

is derived from ethyleneimine. R is preferably hydrogen or methyl, inparticular methyl.

Monomers A of the general formula II can be prepared by reacting anethylenically unsaturated carboxylic acid of the general formula III

where R is as defined above, in particular hydrogen or methyl, with anoligoalkyleneimine, preferably in the form of an oligomer mixture, ofthe general formula IV

where R′ and R″ are as defined above, in particular hydrogen,

is a linear or branched oligoalkyleneimine chain and k is m−1, andsubsequently converting the resulting product with a mineral acid HY inthe acid addition salt of the general formula II.

Preference is given to using the carboxylic acid of the general formulaIII in at least equimolar amounts, in particular in a molar excess,based on the nitrogen atoms of the compound IV. In particular, the molarratios III:IV are selected such that the molar ratio of III to thenumber of nitrogen atoms in IV is in the range from 1.5:1 to about 20:1.

Examples of suitable mineral acids HY are HCl , H₂SO₄ and H₃PO₄ or HNO₃.

The preparation can be carried out both in an aqueous reaction medium ofthe type described above and in an inert organic solvent, preferably ahydrocarbon, in particular an aliphatic hydrocarbon having up to 12carbon atoms.

The reaction of III with IV is preferably carried out in the absence ofoxygen, i.e. under an inert gas atmosphere (e.g. nitrogen or argon)and/or in the presence of customary acrylate stabilizers, e.g. quinonessuch as hydroquinone monomethyl ester.

In the typical reaction of III with IV, the compound of the generalformula IV is added, continuously or batchwise at the reactiontemperature, to a solution of the acid of the general formula III in thedesired solvent. The reaction temperatures for this reaction are usuallyin the range from 10 to 100° C., in particular in the range from 30 to70° C. The acid HY is preferably added after cooling of the reactionmixture to room temperature. Preferred mineral acids HY are the acidsmentioned above: hydrochloric acid, sulfuric acid, phosphoric acid andnitric acid, particular preference being given to hydrochloric acid andsulfuric acid. When working in an organic reaction medium, use is oftenmade of gaseous HCl. For further details of the reaction of compoundsIII and IV reference is made to U.S. Pat. No. 3,336,358 and DE-A 41 30919, in which the reaction of methacrylic acid with ethyleneimine isdescribed. The reaction conditions cited therein are directly applicableto the preparation of the novel esters of the general formula II, sothat these references are incorporated herein by reference.

When the reaction is conducted in an aqueous reaction medium, aqueoussolutions of compounds of the general formula II are obtained—dependingon the starting material IV in the form of pure compounds or oligomermixtures—which still contain the excess acid III. This acid ispreferably separated in the process of the invention prior to using II.However, if polymers comprising acid groups are desired, the acid IIImay completely or partially remain in the solution. The acid III isseparated by generally known methods, e.g. by extraction ordistillation. The resulting aqueous solutions of compounds of theformula II can be employed directly in the polymerization process of theinvention.

When the reaction of compounds of the general formula III with compoundsof the general formula IV is conducted in an apolar, organic solvent,the compound of the general formula II precipitates in the form of asolid, whereas the acid III usually remains dissolved in the organicsolvent. It will be appreciated that the acid III can be recovered fromthe organic solvent and returned to the reaction with IV.

The solutions of the monomers A of formula II, especially the aqueoussolutions, are particularly interesting, as they may be utilizeddirectly in the process according to the invention. An elaborateisolation of these compounds is therefore not required. The solutions ofthese compounds II and in particular their aqueous solutions arecommercially particularly interesting and they are, thus, an object ofthis invention.

In order to stabilize compounds II, in particular in view of anyundesireable polymerization reactions, preferably a stabilizer is addedto the solutions, in particular to the aqueous solutions. Thestabilizers in question are, for example, Broenstedt acids andpreferably the HY acids forming the acid addition salt. In particularthese are hydrochloric acid, formic acid and sulphuric acid. If suchacids are used, the solution to be stabilized is preferably stabilizedwith at least 1, preferably at least 1.5 and most preferably with atleast 1.8, for example 2, acid equivalents, per mole of compound II.

The stabilizers used are particularly those compounds acting asantioxidant and or as a radical trap. Among these are the compoundshaving nitroxyl radicals, such as 2,2,6,6-tetramethyl piperidine-N-oxyl(TEMPO), 4-hydroxy-TEMPO; amino phenols, such as 2-amino phenol; hydroxyphenols, hydroxy phenols substituted by alkyl, their monoalkyl ethers,such as methylhydroquinone, hydroquinone monomethyl ether, hydroquinonemonobenzyl ether, 4-tert-butylcatechol; also phenothiazine andsubstituted phenothiazines; as well as sodium bisulfites. Such compoundsare preferably added in amounts of 10 to 1000 ppm, more preferably 100to 900 ppm and in particular 200 to 500 ppm, based on the weight partsof compounds II in the aqueous solution to be stabilized.

The compounds of the general formula IV which are used as startingmaterials for the preparation of II and have an intact aziridine ringcan be obtained by controlled oligomerization of aziridines of thegeneral formula V,

where R′ and R″ are as defined above.

The oligomerization is conducted in the presence of catalytic amounts ofa Brönstedt acid or a Lewis acid. Examples of Lewis acids aretrialkylaluminum compounds. Preference is given to Brönsted acids havinga pKa of <1, for example the abovementioned mineral acids, in particularhydrochloric acid or sulfuric acid, or strong organic acids such asp-toluenesulfonic acid, trifluoromethanesulfonic acid, trichloroaceticacid or trifluoroacetic acid. The amount of acid is usually in the rangefrom 0.05 to 5% by weight, in particular in the range from 0.1 to 2% byweight, based on aziridine of the general formula V used.

The reaction is usually conducted at temperatures above roomtemperature, preferably at temperatures in the range from 30° C. to 80°C. Temperatures higher than 100° C. are less preferred.

The reaction can be conducted in one of the abovementioned aqueousreaction media or in an organic solvent which is inert under thereaction conditions. Examples of suitable organic solvents areC₁-C₄-alcohols, in particular methanol or ethanol, dialkyl ethers suchas diethyl ether and aliphatic and aromatic hydrocarbons. Particularlypreferred organic solvents are aliphatic hydrocarbons having up to 12carbon atoms. The reaction usually involves slowly introducing thecatalyst and a solution of the aziridine of the general formula V in thedesired solvent into the reaction vessel under reaction conditions. Thereaction vessel usually contains part of the solvent. The reaction timeis usually between 3 min and 10 h. The reaction is usually stopped byneutralizing the acid with a small excess of a strong base, for examplean alkali metal hydroxide or an alkali metal carbonate, in particularwith aqueous sodium hydroxide.

The reaction can be carried out batchwise or continuously. Thecontinuous reaction can be conducted in the reactors customary for thispurpose, preferably in tube reactors or tube bundle reactors. In atypical continuous preparation, a solution of the aziridine of theformula V is mixed with a solution of the desired catalyst in thedesired proportions and the resulting mixture is introduced into areaction zone, for example a flow reactor heated to the reactiontemperature, and the reactor effluent is cooled and subsequentlyneutralized with a base. The reaction time is preferably from 0.5 to 5 hin the case of the batch process and from 3 min to 30 min in the case ofthe continuous process.

The degree of oligomerization can be controlled in a simple manner viathe reaction temperature and the reaction time, with an increase intemperature or a long reaction time leading to high degrees ofoligomerization. Higher temperatures lead to more highly branchedproducts IV.

The abovementioned processes produce solutions of the oligomers in thesolvent used in each case. It is possible to isolate the oligomer of thegeneral formula IV from this solvent. However, preference is given tousing the solutions of the oligomers IV for the preparation of compoundsof the general formula II without any further workup.

Another aspect of the present invention is the use of the water-solublepolymers of the present invention as auxiliaries in papermaking.

The novel water-soluble polymers having oligoalkyleneimine side chainsof the general formula I are particularly suitable as draining aids,flocculents and retention aids and as fixing agents in papermaking. Forthis purpose, they are added to the respective paper stock in an amountof from 0.01 to 2% by weight, preferably in an amount of from 0.01 to0.5% by weight, e.g. from 0.01 to 0.1% by weight, in each case based onthe solids present in the paper stock.

In particular, the homopolymers and copolymers of the invention lead toan improved retention of fines compared to the prior art polymers. Theyhave been found particularly useful in the retention of fillers such ascalcium carbonate. The homopolymers are particularly known for theirgood fixing properties.

The water-soluble polymers of the invention can be used for making allgrades of paper, paperboard and cardboard, for example paper fornewsprint (letter press/offset printing), medium-fine writing andprinting paper, imitation intaglio printing paper and also lightweightcoating base paper. These grades of paper are produced from ground wood,thermomechanical pulp (TMP), chemothermomechanical pulp (CTMP), pressureground wood (PGW) or sulfite or sulfate pulp, which may each be short-or long-fibered. Further suitable raw materials for the production ofthe paper stock are also chemical pulp and mechanical pulp, which arefurther processed in integrated mills directly in more or less moistform, without prior thickening or drying, to give the paper. Some ofthese materials still contain residual impurities from the digestionstage which greatly impair the conventional papermaking process. Theseimpurities are particularly well fixed on the paper by the polymers ofthe invention.

The use of the polymers of the invention makes it possible to prepareboth filler-free and filler-containing papers. The filler content offiller-containing papers can be up to a maximum of 40% by weight and ispreferably in the range from 5 to 30% by weight. Examples of suitablefillers are clay, kaolin, chalk, talc, titanium dioxide, calciumsulfate, barium sulfate, aluminum oxide, satin white or mixturesthereof.

The good fixing action is particularly useful in the production of paperfrom waste paper and from material systems which contain interferingsubstances which accumulate in partially or completely closed watercirculations of paper machines.

EXAMPLES Analytical Methods

The viscosity was determined in accordance with Brookfield at 25° C.using a Brookfield viscometer and aqueous solutions of the polymers.

The average molecular weight was determined by light scattering by meansof dynamic and static light scattering using an ALV goniometer and anALV 5000 correlator. Solutions of the polymers in 0.1 molar NaClsolution were analyzed at 25° C. and a polymer concentration of 0.1-0.4g/l.

The cationic charge density was determined by titration with potassiumpolyvinylsulfate in accordance with D. Horn, Progr. Colloid u. PolymerSci. 65 (1978) 251.

The molecular weight of the oligomers of the general formula IV wasdetermined titrimetrically by opening the aziridine ring in IV using anexcess of HBr in glacial acetic acid and back-titration of the excessHBr with silver nitrate.

The K value of the polymers of the invention was determined inaccordance with Fickentscher by measuring the viscosity of 0.1% strengthby weight solutions of the polymers in 5% strength by weight NaClsolution.

II Preparation Examples

1. Oligomerization of Ethyleneimines to Give Oligomers of the Formula IV(Preparation Examples 1a to 1c)

Preparation Example 1a

A reactor equipped with a reflux condenser and 2 dropping funnels wascharged with 55.8 g of water and heated to 55° C. At this temperature,369.8 g of a 45% strength by weight aqueous solution of ethyleneimineand 44.0 g of a 3.4% strength by weight aqueous hydrochloric acid wereintroduced into the polymerization vessel in the course of one hour,beginning at the same time. The mixture was then held at thistemperature for 3 h with stirring, cooled to room temperature andadmixed with a solution of 1.82 g of NaOH in 4 g of water. 475 g of a35% strength by weight aqueous solution of an ethyleneimine oligomerwere obtained. The aziridine ring content, based on the oligomer, was5.62 mmol/g. The average molecular weight calculated therefrom was 177g/mol. This corresponds to an average {overscore (m)} of about 4.1.

Preparation Example 1b (Continuous Oligomerization of Ethyleneimine inWater)

A tube reactor (600 cm length, 0.6 cm internal diameter, stainlesssteel) heated to 70° C. was fed in parallel via a static mixer with a27% strength by weight aqueous ethyleneimine solution and a 4.83%strength by weight aqueous hydrochloric acid in a weight ratio of11.2:1. The total volume flow was 1.13 kg/h. The reactor effluent wascooled to 10° C. and neutralized with a 10% strength by weight excess ofaqueous sodium hydroxide solution via a static mixer. In this way, a24.4% strength by weight aqueous solution of an ethyleneimine oligomerwas obtained which had a titrimetrically determined aziridine ringcontent of 13.9 mmol/g. The number average molecular weight calculatedtherefrom was 72 g/mol (corresponding to an {overscore (m)} value of1.67).

Preparation Example 1c (Oligomerization of Ethyleneimine in Octane)

A reactor equipped with reflux condenser and 2 dropping funnels wascharged with 40 g of n-octane and heated to 65° C. While maintaining thetemperature, 360.2 g of a 55% strength by weight solution ofethyleneimine in n-octane and 96 g of a 1.2% strength by weight solutionof H₂SO₄ in n-octane were added in the course of one hour, beginning atthe same time. The mixture was maintained at this temperature for afurther hour, cooled to room temperature and neutralized with a 10 mol %excess of aqueous sodium hydroxide solution, and resulting sodiumsulfate was filtered off, yielding 495.8 g of a 40% strength by weightsolution of the ethyleneimine oligomer in octane. The oligomer had anaziridine ring content of 6.49 mmol/g. The number average molecularweight calculated therefrom was 154 g/mol, corresponding to an{overscore (m)} value of 3.58.

2. Preparation of Compounds of the General Formula II

Preparation Example 2a (Preparation in Water)

A reaction vessel equipped with a reflux condenser, a dropping funneland a pH measurement device was charged with 254 g of methacrylic acidheated to 55° C. 130 g of the ethyleneimine oligomer solution obtainedin Example 1b were then added dropwise in the course of 2 h. After afurther 30 min at 55° C., the mixture was cooled to 15° C. and themixture was adjusted to a pH of 1 using 68.7 g of a 37% strength byweight aqueous hydrochloric acid. 100 ml of n-octane were added, thephases were separated and the aqueous phase was washed five times with50 ml of n-octane each time. In this way, 232 g of a 40.4% strength byweight aqueous solution of the oligoaminoethyl methacrylatehydrochloride (II) were obtained.

Preparation Example 2b (Reaction in n-Octane)

A reaction vessel equipped with a reflux condenser, a dropping funneland a gas inlet was charged with 800 g of methacrylic acid and 800 g ofoctane and heated to 60° C. 496 g of the 40% strength by weightethyleneimine oligomer solution in n-octane obtained in Example 1c wereadded in the course of 3 h. After addition was complete, the mixture wasmaintained at the abovementioned temperature for a further hour andcooled to 30° C. At this temperature, 175 g of gaseous HCl wereintroduced, leading to phase separation. After separation of the upperphase, which essentially consisted of octane and excess methacrylicacid, the lower phase was washed with 200 ml of octane. The semisolidlower phase was then stirred with 500 ml of acetone, yielding thecompound of the general formula II in the form of its hydrochloride as asolid which was filtered off. The yield was 391.4 g.

3. Stabilization of the Solutions of Formula II

To improve the storage stability, the aqueous solutions were mixed withsmall amounts of phenothiazine or 4-tert-butylcatechol. By measuring theviscosity of the solutions and by means of gel permeation chromatographyit was determined whether an increase in molecular weight took placewhich would indicate a decomposition of the compounds II. Theunstabilized solution was used as a reference.

Stabilization Example 1 (Phenothiazine)

52.5 g of the 40% solution from example 2a were mixed with 34.3 mg of a14.3% by weight solution of phenothiazine in acetone (corresponding to4.9 mg of phenothiazine or 234 ppm, based on compound II) and stored atroom temperature for 6 weeks.

Stabilization Example 2 (4-tert-Butylcatechol)

52.7 g of the 40% solution from example 2a were mixed with 16.6 mg of a31% by weight solution of 4-tert-butylcatechol in acetone (correspondingto 5.2 mg of 4-tert-butylcatechol or 224 ppm, based on compound II) andstored at room temperature for 6 weeks.

In comparison to the reference sample, the samples from stabilizingexamples 1 and 2 did neither show any increase in viscosity nor a changeat GPC (chromatography at polyhydroxy methacrylate (HEMA-Bio of PSSGmbH, 14% aqueous formic acid as eluting agent) in the limits ofmeasuring tolerances, which indicates the nonoccurence of an undesiredincrease in molecular weight.

PREPARATION OF THE COPOLYMERS OF THE INVENTION Example 1Copolymerization of II from 2a with Acrylamide in Aqueous Solution;Acrylamide:II=82:18

The reaction vessel is charged with 655 g of water, 130.9 g of a 50%strength by weight aqueous acrylamide solution, 0.1 ml of Trilon® C and35.9 g of the 40.4% strength by weight aqueous solution of compound IIobtained in Example 2a and heated to 37° C. 0.02 g of

2,2′-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride in 20 g ofwater was introduced into the reaction vessel while maintaining thetemperature. After 2 h, an identical amount of initiator was added, andthe reaction temperature was maintained for a further 3 h. During thistime, the mixture was diluted by portionwise addition of a total of 900g of water. The mixture was then heated to 50° C. and admixed with asolution of 0.02 g of

2,2′-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride in 20 g ofwater, and the temperature was maintained for a further 2 hours. Theaqueous solution of the copolymer of the invention obtained in this wayhad a solids content of 4.7% by weight. The properties of the copolymerare listed in Table 1.

Example 2 Copolymerization of II from 2b with Acrylamide in AqueousSolution; Acrylamide:II=75:25

A polymerization vessel was charged with 406 g of water, 45 g ofacrylamide solution (50% strength by weight), 0.1 ml of Trilons® C, 5 gof a 10% strength by weight aqueous formic acid solution and 7.5 g ofthe hydrochloride II obtained in Example 2b and heated to 37° C. Asolution of 0.0125 g of

2,2′-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride in 10 g ofwater was added, and the temperature was maintained for 2 hours. Thisprocedure was repeated twice. Two hours after the last initiatoraddition, a solution of 0.075 g of

2,2′-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride in 10 g ofwater was added, and the temperature was maintained for a further 2hours. During this time, a total of 500 g of water was introduced intothe polymerization vessel. After cooling, an aqueous solution having asolids content of 3.3% by weight was obtained. The properties of thecopolymer are listed in Table 1.

Example 3 Copolymerization of II from 2b with Acrylamide in AqueousSolution

A polymerization reactor was charged with 406 g of water, 39 g ofaqueous acrylamide solution (50% strength by weight), 10.5 g of thehydrochloride obtained in Preparation Example 2b and 0.1 ml of Trilon® Cand heated to 37° C. The mixture was admixed three times, in 2 hintervals, with a solution of 0.0125 g of

2,2′-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride in 10 ml ofwater each time. After a further 2 h, a further 0.075 g of2,2′-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride dissolved in 10ml of water were added. In the course of the reaction, an additionaltotal of 500 ml of water was added. The polymerization is complete aftera further 2 h. The resulting polymer solution had a polymer content of3.0% by weight.

Example 4 Homopolymerization of Monomer II from 2b in Aqueous Solution

A polymerization vessel was charged with 350 g of water and 100 g of thehydrochloride obtained in Preparation Example 2b and heated to 37° C. Asolution of 0.3 g of

2,2′-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride in 50 ml ofwater was added in the course of 5 h. After addition was complete, thetemperature was maintained for a further 3 h. The mixture was thenheated to 50° C., and the temperature was maintained for a further 3 h.During this time, the reaction mixture was diluted by portionwiseaddition of a total of 500 ml of water. The resulting polymer solutionhad a solids content of 10% by weight.

Example 5 Copolymerization in W/O Emulsion

A polymerization reactor equipped with a centrally arranged propellerstirrer was charged with 315 g of a 60% strength by weight acrylamidesolution, 156 g of the 40.4% strength by weight aqueous solution ofhydrochloride II obtained in Example 2a and 0.1 ml of Trilon® C. Asolution of 40.5 g sorbitan monooleate (Span®R80) in 500 g of paraffinoil (boiling point about 200° C., Isopar®M) was added. A W/O emulsionwas prepared from this mixture by intensive stirring (1000 rpm) for 30min, and nitrogen was passed through the emulsion to remove traces ofoxygen. A solution of 0.3 g of 2,2′-azobis(2,2-valeronitrile) in 10 g ofparaffin was then added, and the mixture is heated to 45° C. and held atthis temperature for 5 h. In this way, an emulsion having a polymercontent of 24.6% by weight was obtained.

Trilon® C is a 40% strength by weight solution of pentasodiumdiethylenetriaminepentaacetate

TABLE 1 Cationic charge K Viscosity²⁾ M_(W) ³⁾ density⁴⁾ [meq/g] Examplevalue¹⁾ [mPas] [g/mol] pH 3.5 pH 7 1 212 2360 15 · 10⁶ 1.5 1.1 2 1751050 n.d. 1.9 1.2 46,000* 3 178 1220 n.d. 3.2 2.0 4 107 n.d. n.d. 8.55.5 C1 n.d. 450** 1.5 · 10⁶ 2.5 0.3 (pH 5) ¹⁾In accordance withFickentscher (0.1% by weight in 5% strength NaCl solution) ²⁾Brookfieldviscosity; 1% strength by weight solution, 25° C. or *6% strength byweight solution or **10% strength by weight solution ³⁾Weight averagemolecular weight, light scattering ⁴⁾Determined in accordance with D.Horn by titration with potassium polyvinylsulfate

Comparative Example VI

A reaction vessel was charged with 100 g of a 20% strength by weightaqueous acrylic acid solution and inertized with nitrogen. 0.04 g ofperoxodisulfate and 0.04 g of NaHSO₃ were then added, and the mixturewas heated to 50° C. for 4 h. The resulting polyacrylic acid solutionwas admixed with 73 g of water and 6 g of ethyleneimine at roomtemperature and then heated to 50° C. for 2 h. 10.1 g of a concentratednitric acid (61% strength by weight) were added, and the temperature wasmaintained for a further 30 min. Another 6 g of ethyleneimine wereadded, and after a further hour 10.1 g of concentrated nitric acid wereadded, and the temperature was maintained for a further 30 min. In thisway, a solution with a polymer content of 15.6% by weight was obtained.

PERFORMANCE RESULTS Investigation of the Retention Properties of theCopolymers of the Invention.

Retention tests were carried out using a Dynamic Drainage Jar (TappiStandard T-261). The apparatus has been described by K. W. Britt, J. E.Unbehend: New Methods for Monitoring Retention, Tappi Journal, Vol. 59,1976, p. 67-70. In all tests, the starting material was a paper stock of40% of pine sulfate pulp, 40% of birch sulfate pulp and 20% of calciumcarbonate having a consistency of 5.51 g/l which was composed of 3.54 gof long fibers, 0.97 g of fines and 1.00 g of solids which cannot beashed (ash fraction). The freeness was 35° SR.

1. Polymer Testing Without Microparticles

500 ml of the paper stock were introduced into a Dynamic Drainage Jarand stirred at 1000 rpm for 10 sec. The respective polymer was added inthe form of a 0.02% strength by weight aqueous solution, and the mixturewas stirred at 1000 rpm for another 60 sec. A value of 100 ml was thentaken off at the outlet of the apparatus and filtered via a white ribbonfilter. The weight of the dry filter cake was used to calculate thetotal retention (First Pass Retention). The heavier the filter cake, thepoorer the retention properties of the polymers. For comparison, thetest was also conducted without addition of a polymer. Amounts used andresults are summarized in Table 2. The filter was then ashed at 500° C.The ash fraction found was used to determine the first pass ashretention which corresponds to the amount of filler retained. Thedifference is the fines retention. The results are likewise summarizedin Table 2.

TABLE 2 Polymer Exam- [% by Solids FPR²⁾ Ash FPAR³⁾ Test No. pleweight]¹⁾ [mg] [%] [mg] [%] C1* — — 124 77.5 95 5.0 2 2 0.01 117 78.8 8614.0 3 2 0.02 98 82.2 73 27.0 4 2 0.04 96 82.6 65 35.0 5 3 0.01 134 75.791 9.0 6 3 0.02 110 80.0 75 25.0 7 3 0.04 102 81.5 65 35.0 C8* C1 0.01120 78.2 93 7.0 C9* C1 0.02 123 77.7 92 8.0 C10* C1 0.04 127 77.0 93 7.0¹⁾% by weight of polymer, based on solids content in pulp ²⁾FPR: totalretention (First Pass Retention) ³⁾FPAR: ash retention (First Pass AshRetention) *Comparative tests

2. Investigation of Retention Effect of the Polymers in the Presence ofMicroparticles (Bentonite)

500 ml of the paper stock described in 1. were introduced into a DynamicDrainage Jar and then stirred at 1500 rpm for 10 sec. 5.5 ml of a 0.02%strength by weight aqueous solution of the respective polymer wereadded, and the mixture was stirred at 1500 rpm for 60 sec. Theproportion of the polymer, based on solids in the pulp, was 0.04% byweight. The stirring speed was reduced to 1000 rpm, and 0.3 ml or 0.6ml, respectively, of a 2% strength by weight suspension of bentonite(Hydrocoll OT, cf. EP-A 235 893) in water were added, and the mixturewas stirred at 1000 rpm for another 30 sec. 100 ml of liquid were thentaken off at the outlet of the apparatus and filtered via a white ribbonfilter. Total retention and ash retention were determined as describedin 1. The results are summarized in Table 3.

TABLE 3 Bento- Polymer nite [% Test Exam- [% by by Solids FPR²⁾ AshFPAR³⁾ No. ple weight]¹⁾ weight] [mg] [%] [mg] [%] C11* — — — 126 77.192 8.0 12 2 0.04 0.2 91 83.5 54 46.0 13 2 0.04 0.4 84 84.8 54 46.0 14 30.04 0.2 95 82.8 60 40.0 15 3 0.04 0.4 91 83.5 58 42.0 C16* C1 0.04 0.2119 78.4 82 18.0 C17* C1 0.04 0.4 120 78.2 91 9.0 ¹⁾% by weight ofpolymer, based on solids content in pulp ²⁾FPR: total retention (FirstPass Retention) ³⁾FPAR: ash retention (First Pass Ash Retention)*Comparative tests

3. Investigation of Retention Action of the Polymers of the Invention inthe Presence of Bentonite in a Paper Stock Which Comprises PolyaluminumChloride (PAC).

The paper stock described in 1. and 2. was modified to contain, inaddition to the birch sulfate pulp, the pine sulfate pulp and thefiller, 2% by weight of polyaluminum chloride (commercial product),based on the abovementioned constituents.

The investigation was carried out as described in 2., i.e. 500 ml ofpaper stock, polymer and bentonite were in each case combined asdescribed in 2. and stirred under the conditions described in 2.

Materials used and total retention and ash retention found are listed inTable 4.

TABLE 4 Bento- Polymer nite [% Test Exam- [% by by Solids FPR²⁾ AshFPAR³⁾ No. ple weight]¹⁾ weight] [mg] [%] [mg] [%] C18* — — — 123 77.794 6.0 19 2 0.04 0.2 102 81.5 66 34.0 20 2 0.04 0.4 107 80.6 68 32.0 213 0.04 0.2 106 80.8 70 30.0 22 3 0.04 0.4 110 80.0 70 30.0 C23* C1 0.040.2 122 77.9 90 10.0 C24* C1 0.04 0.4 125 77.3 91 9.0 ¹⁾% by weight ofpolymer, based on solids content in pulp ²⁾FPR: total retention (FirstPass Retention) ³⁾FPAR: ash retention (First Pass Ash Retention)*Comparative tests

We claim:
 1. A process for preparing water-soluble copolymers havingoligoalkyleneimine side chains of formula I,

where

is a linear or branched oligoalkyleneimine chain comprising malkyleneimine units, where m is an integer from 1 to 20, and the numberaverage of m in the oligoalkyleneimine side chains is at least 1.5, Y isthe anion equivalent of a mineral acid, and x is 0≦x≦m,  which comprisescopolymerizing ethylenically unsaturated monomers M, comprising: from 5to 50% by weight of at least one monomer A of formula II or an oligomermixture thereof

 where

m and Y are as defined above, R is hydrogen or C₁-C₄-alkyl, and n is1≦n≦m; and from 50 to 95% by weight of at least one neutral or cationic,water-soluble monomer B which is monoethylenically unsaturated, and upto 10% of one or more monomer C which are different from said monomers Aand said water-soluble, monoethylenically unsaturated monomers B, in anaqueous polymerization medium in the presence of an initiator whichtriggers the free-radical polymerization of the monomers M.
 2. Theprocess as claimed in claim 1, wherein the monomers to be polymerized donot comprise any monomers C.
 3. The process as claimed in claim 1,wherein R in formula II is methyl.
 4. The process as claimed in claim 1,wherein the oligoalkyleneimine chain

is derived from ethyleneimine.
 5. The process as claimed in claim 1,wherein the monomers A comprise an oligomer mixture comprising less than25% by weight, based on the total weight of the monomers A, of compoundsof the formula II where m=1.
 6. The process as claimed in claim 1,wherein the sole monomer B used is acrylamide.
 7. The process as claimedin claim 1, wherein the polymerization is carried out in water.
 8. Theprocess as claimed in claim 1, wherein the polymerization is carried outin an aqueous polymerization medium, which is dispersed in the form of awater-in-oil emulsion in a liquid organic medium which is inert towardthe polymerization conditions.
 9. A copolymer having oligoalkyleneimineside chains of the formula I as defined in claim 1 and a weight averagemolecular weight M_(W)≦2,000,000, which comprises from 5 to 50% byweight of at least one monomer A, from 50 to 95% by weight of at leastone neutral or cationic; water-soluble monomer B which aremonoethylenically unsaturated, and, optionally up to 10% of at least onemonomer C which are different from said monomers A and water-soluble,monoethylenically unsaturated monomers.
 10. The copolymer as claimed inclaim 9, comprising only monomers A and B.
 11. The homopolymer havingoligoalkyleneimine side chains of the formula I as defined in claim 1,which is exclusively composed of the monomers A.
 12. The copolymer asclaimed in claim 9, wherein the number average of m is in the range from2.1 to
 8. 13. The copolymer as claimed in claim 9, wherein structuralunits derived from monomers A of the formula II where m=1 are present ina proportion of less than 25% by weight, based on the total weight ofall structural units derived from monomer units A.
 14. A monomer mixtureof formula II

where R,

Y and n are as defined in claim 1 and the number average of m is atleast 2.1.
 15. An aqueous monomer solution comprising at least onemonomer or a monomer mixture of claim
 14. 16. The homopolymer as claimedin claim 11, wherein the number average of m is in the range from 2.1 to8.
 17. The homopolymer as claimed in claim 11, wherein structural unitsderived from monomers A of the formula II where m=1 are present in aproportion of less than 25% by weight, based on the total weight of allstructural units derived from monomer units A.
 18. A method of makingpaper from paper stock, said method comprising adding at least onecopolymer as defined in claim 9 to said paper stock.
 19. A method ofmaking paper from paper stock, said method comprising adding at leastone homopolymer as defined in claim 11 to said paper stock.